In Dutcher U.S. Pat. No. 4,217,913 and Gold U.S. Pat. No. 4,463,765 body implantable leads particularly for carrying electrical impulses to stimulate and regulate the heart muscle are disclosed. The specific leads each define fixation means which comprises an initially retracted, advanceable corkscrew pin which, after positioning of a forward electrode on the lead in the desired position, may be advanced into the tissue of the heart, or other tissue as desired, to retain the electrode and its lead in the appropriate position.
The fixation means is advanced and retracted by a drive mechanism which includes driver coil means extending the length of the lead and connected at the outer or proximal end of the lead assembly to the terminal pin. Thus, the terminal pin provides the double function of being capable of connection to the source of heart muscle-stimulating electrical power, but it also constitutes a handle which can be rotated to advance or retract the fixation means positioned at the other end of the lead.
In the prior designs, problems have been encountered because of the rotatable nature of the terminal pin. In the prior designs, difficulties have arisen in the maintenance of a good electrical connection between the terminal pin and the electrical wire or wires in the lead, with the problem centering on the fact that the terminal pin is rotatably movable with respect to the electrical wire, which tends to be fixed and non-rotatable. Significant electrical resistance can develop in the long term use of a cardiac pacer-lead at the junction between the stationary electrically conductive parts connected to the wire or wires, and the rotatable part or parts connected to the terminal pin. It is of course a matter of great criticality for the lead to maintain an undiminished electrical connection between the terminal pin and the distal electrode within the body, positioned typically against or in the heart. A failure of electrical connection, of course, causes a complete failure of the pacer itself.
By this invention an improved electrical connection is provided between the terminal pin and the electrical wire which communicates with the distal electrode, for increased reliability of active fixation type leads, in which the terminal pin is rotatable for moving the fixation means between its retracted, nonaffixing and its affixing positions